1. Field
The following description relates to an apparatus and method for reducing digital noise generated upon Analog-to-Digital (AD) conversion or lossy coding, using reverberation.
2. Discussion of Related Art
Since the 1990's, digital audio formats such as MP3 have been popularized. Digital audio formats such as MP3 have an advantage of allowing people to listen to the music with a small capacity since they are efficiently compressed, however, the digital audio formats have a disadvantage that they have quantization noise since they are digital signals, and also digital noise is added when audio signals are compressed.
Quantization noise (error) is generated when an analog signal is converted to a digital signal (Analog-to-Digital (AD) conversion). A representative digital conversion method is pulse code modulation (PCM). PCM performs conversion by a three-step process of sampling, quantization, and encoding as follows. In the sampling, successive analog signals are sampled at regular time intervals to generate pulse amplitude modulation (PAM) signals. In the quantization, the sampled signals are digitized. For example, quantization means representing a sampled value as the nearest value among values of predetermined levels divided in advance. During quantization, there is a difference between the analog signal value and the digitized signal value, which is called a quantization error. A finally quantized value is subject to binary encoded to thereby be converted into a digital signal.
Also, since a signal such as an MP3 signal, subject to lossy compression, cannot be decoded to its exact original signal, noise is generated upon lossy encoding and decoding. In the case of lossy encoding, generally, more digital noise is generated in high-frequency region than in low-frequency region.
As such, a digital audio source may include digital noise due to digital conversion or lossy encoding. The digital noise has random characteristics. In the case of lossy encoding, a random characteristic to which a weight is reflected according to a weight for each frequency band that is applied upon encoding, may appear. Digital noise which does not exist in natural analog audio sources deteriorates the quality of digital audio sources, and increases listening fatigue. That is, digital noise causes unpleasant noise when a digital signal is reproduced, and as such noise is greater, a listener suffers from listening fatigue when he or she listens to digital music (for example, MP3 music). Accordingly, in order to reduce listening fatigue, a method capable of reducing digital noise is needed.